The motives for the killings were not immediately known, and few such cases in Mexico are ever solved. But human rights groups condemned the deaths as another worrying sign of the vulnerability of journalists reporting on the wave of drug and organized crime violence that has rocked Mexico in the past six years and left more than 50,000 people dead.

“What we have seen in Mexico in the last years is a systematic attempt to muzzle the press that has been successful in various parts of the country, where the press has been effectively censored,” said Rosental Alves, director of the Knight Center for Journalism in the Americas, in Austin, Tex. “This unprecedented blood bath is fueled by a certainty of impunity, as the cases of crimes against the press usually don’t even reach a court of law.”

The Veracruz journalists killed this past week were the first documented killings of Mexican journalists this year, according to press groups; last year, 11 were killed and, according to Article 19, a press freedom group, 44 have been killed in the past six years as drug crime soared and the government began an offensive.

The criminal gangs are known to use bribes and death threats to dictate coverage or suppress it. The authorities have also suggested that some journalists themselves have worked for the cartels, though the Committee to Protect Journalists, a watchdog group in New York, said there was little evidence to support such claims.

Two of the journalists whose bodies were discovered Thursday, wrapped in plastic bags in a canal in Boca del Río, were identified as Gabriel Huge and Guillermo Luna, who had both worked for Notiver, a local newspaper, before leaving the state for their own safety. They had recently returned to work for VeracruzNews. The third was Esteban Rodríguez, who worked as a cameraman for TV Azteca and most recently as a photographer for Diario AZ. The body of Irasema Becerra, Mr. Luna’s girlfriend, was found with him.

Notiver covers a state rapidly becoming one of Mexico’s most violent. Last June, Miguel Ángel López Velasco, a columnist and the newspaper’s editorial director, was shot to death along with his wife and one of his children. A month later, Yolanda Ordaz de la Cruz, one of the newspaper’s police reporters, was found with her throat slit.

On Saturday, Regina Martínez, the reporter who worked for the magazine Proceso and had written on ties between the local police and organized crime, was found beaten and strangled in her house in the capital of Veracruz, Xalapa. “They have all been witnesses to the decomposition that has been occurring there,” said Ricardo González, a protection officer for Article 19.

The bodies of the three photojournalists were discovered on World Press Freedom Day and less than a week after Mexico’s Congress approved a law granting protection to journalists who have received threats.

A version of this article appears in print on May 4, 2012, on page A12 of the New York edition with the headline: Photographers Found Dead In Mexico. Order Reprints|Today's Paper|Subscribe